The changes in the carrying amount of goodwill for the years ended December 31, 2019 and 2018, are as follows:


(in millions)	Goodwill

Historical goodwill	$	12,449
Goodwill from acquisition of Layer3 TV	218
Accumulated impairment losses at December 31, 2018	(10,766)

Balance as of December 31, 2018	1,901
Goodwill from acquisition in 2019	29

Balance as of December 31, 2019	$	1,930
Accumulated impairment losses at December 31, 2019	$	(10,766)

In July 2019, we completed our acquisition of a mobile marketing company, for cash consideration of $32 million. Upon closing of the transaction, the acquired company became a wholly-owned consolidated subsidiary to T-Mobile. We recorded Goodwill of approximately $29 million, calculated as the excess of the purchase price paid over the fair value of net assets acquired. The acquired goodwill was allocated to our wireless reporting unit and will be tested for impairment at this level.

The assets acquired and liabilities assumed were not material to our Consolidated Balance Sheets. The financial results from the acquisition closing date through December 31, 2019 were not material to our Consolidated Statements of Comprehensive Income. The acquisition was not material to our prior period consolidated results on a pro forma basis.

The following table summarizes our spectrum license activity for the years ended December 31, 2019 and 2018:


(in millions)	2019		2018
Spectrum licenses, beginning of year	$	35,559	$	35,366

Spectrum license acquisitions	857		138
Spectrum licenses transferred to held for sale	—		(1)
Costs to clear spectrum	49		56

Spectrum licenses, end of year	$	36,465	$	35,559

The following is a summary of significant spectrum transactions for the year ended December 31, 2019:

•In June 2019, the FCC announced that we were the winning bidder of 2,211 licenses in the 24 GHz and 28 GHz spectrum auctions for an aggregate price of $842 million.

•At the inception of the 28 GHz spectrum auction in October 2018, we deposited $20 million with the FCC. Upon conclusion of the 28 GHz spectrum auction in February 2019, we made an additional payment of $19 million for the purchase price of licenses won in the auction.

•At the inception of the 24 GHz spectrum auction in February 2019, we deposited $147 million with the FCC. Upon conclusion of the 24 GHz spectrum auction in June 2019, we made an additional payment of $656 million for the purchase price of licenses won in the auction.

The licenses are included in Spectrum licenses as of December 31, 2019, in our Consolidated Balance Sheets. Cash payments to acquire spectrum licenses and payments for costs to clear spectrum are included in Purchases of spectrum licenses and other intangible assets, including deposits in our Consolidated Statements of Cash Flows for the year ended December 31, 2019.

The following is a summary of significant spectrum transactions for the year ended December 31, 2018:

•We recorded spectrum licenses received as part of our acquisition of the remaining equity interest in Iowa Wireless Services, LLC, at their estimated fair value of approximately $87 million.

•We closed on multiple spectrum purchase agreements in which we acquired total spectrum licenses of approximately $50 million for cash consideration.

•In 2018, we signed a reciprocal long-term lease arrangement with Sprint in which both parties have the right to use a portion of spectrum owned by the other party. This executory agreement does not qualify as an acquisition of spectrum licenses, and we have not capitalized amounts related to the lease. The reciprocal long-term lease is a distinct transaction from the Merger.

Our impairment assessment of goodwill and other indefinite-lived intangible assets (spectrum licenses) resulted in no impairment as of December 31, 2019 and 2018.


	Useful Lives	December 31, 2019															December 31, 2018
(in millions)				Gross Amount			Accumulated Amortization			Net Amount			Gross Amount			Accumulated Amortization			Net Amount

Customer lists	Up to 6 years	$	1,104		$	(1,104)		$	—		$	1,104		$	(1,086)		$	18
Trademarks and patents	Up to 19 years	323			(258)			65			312			(225)			87
Other	Up to 28 years	100			(50)			50			149			(56)			93

Other intangible assets		$	1,527		$	(1,412)		$	115		$	1,565		$	(1,367)		$	198

Amortization expense for intangible assets subject to amortization was $82 million, $124 million and $163 million for the years ended December 31, 2019, 2018 and 2017, respectively.

The estimated aggregate future amortization expense for intangible assets subject to amortization are summarized below:


(in millions)	Estimated Future Amortization
Year Ending December 31,

2020	$	83
2021	14
2022	3
2023	3
2024	3
Thereafter	9

Total	$	115